Metal species surface treatment of thin film photovoltaic cell and manufacturing method

ABSTRACT

A method for forming a thin film photovoltaic device. The method includes providing a transparent substrate including a surface region. A first electrode layer is formed overlying the surface region. A copper layer is formed overlying the first electrode layer and an indium layer overlying the copper layer to form a multi-layered structure. The method subjects at least the multi-layered structure to a thermal treatment process in an environment containing a sulfur bearing species and form a copper indium disulfide material. The copper indium disulfide material includes a thickness of substantially copper sulfide material. The thickness of the copper sulfide material is removed to expose a surface region having a copper poor surface characterized by a copper to indium atomic ratio of less than about 0.95:1. The method subjects the copper poor surface to a metal cation species to convert the copper poor surface from an n-type semiconductor characteristic to a p-type semiconductor characteristic. A window layer is formed overlying the copper indium disulfide material.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/101,127, filed Sep. 29, 2008, entitled “METAL SPECIES SURFACETREATMENT OF THIN FILM PHOTOVOLTAIC CELL AND MANUFACTURING METHOD” byinventor HOWARD W. H. LEE, commonly assigned and incorporated byreference herein for all purposes. This application is related to U.S.Provisional Patent Application No. 61/101,128 filed Sep. 29, 2008,commonly assigned and incorporated by reference herein for all purposes.This application is related to U.S. patent application Ser. No.12/567,711 filed Sep. 25, 2009, commonly assigned and incorporated byreference herein for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

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REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

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BACKGROUND OF THE INVENTION

The present invention relates generally to photovoltaic materials andmanufacturing method. More particularly, the present invention providesa method and structure for manufacture of high efficiency thin filmphotovoltaic cells. Merely by way of example, the present method andmaterials include absorber materials made of copper indium disulfidespecies, copper tin sulfide, iron disulfide, or others for singlejunction cells or multi junction cells.

From the beginning of time, mankind has been challenged to find way ofharnessing energy. Energy comes in the forms such as petrochemical,hydroelectric, nuclear, wind, biomass, solar, and more primitive formssuch as wood and coal. Over the past century, modern civilization hasrelied upon petrochemical energy as an important energy source.Petrochemical energy includes gas and oil. Gas includes lighter formssuch as butane and propane, commonly used to heat homes and serve asfuel for cooking Gas also includes gasoline, diesel, and jet fuel,commonly used for transportation purposes. Heavier forms ofpetrochemicals can also be used to heat homes in some places.Unfortunately, the supply of petrochemical fuel is limited andessentially fixed based upon the amount available on the planet Earth.Additionally, as more people use petroleum products in growing amounts,it is rapidly becoming a scarce resource, which will eventually becomedepleted over time.

More recently, environmentally clean and renewable sources of energyhave been desired. An example of a clean source of energy ishydroelectric power. Hydroelectric power is derived from electricgenerators driven by the flow of water produced by dams such as theHoover Dam in Nevada. The electric power generated is used to power alarge portion of the city of Los Angeles in California. Clean andrenewable sources of energy also include wind, waves, biomass, and thelike. That is, windmills convert wind energy into more useful forms ofenergy such as electricity. Still other types of clean energy includesolar energy. Specific details of solar energy can be found throughoutthe present background and more particularly below.

Solar energy technology generally converts electromagnetic radiationfrom the sun to other useful forms of energy. These other forms ofenergy include thermal energy and electrical power. For electrical powerapplications, solar cells are often used. Although solar energy isenvironmentally clean and has been successful to a point, manylimitations remain to be resolved before it becomes widely usedthroughout the world. As an example, one type of solar cell usescrystalline materials, which are derived from semiconductor materialingots. These crystalline materials can be used to fabricateoptoelectronic devices that include photovoltaic and photodiode devicesthat convert electromagnetic radiation into electrical power. However,crystalline materials are often costly and difficult to make on a largescale. Additionally, devices made from such crystalline materials oftenhave low energy conversion efficiencies. Other types of solar cells use“thin film” technology to form a thin film of photosensitive material tobe used to convert electromagnetic radiation into electrical power.Similar limitations exist with the use of thin film technology in makingsolar cells. That is, efficiencies are often poor. Additionally, filmreliability is often poor and cannot be used for extensive periods oftime in conventional environmental applications. Often, thin films aredifficult to mechanically integrate with each other. These and otherlimitations of these conventional technologies can be found throughoutthe present specification and more particularly below.

From the above, it is seen that improved techniques for manufacturingphotovoltaic materials and resulting devices are desired.

BRIEF SUMMARY OF THE INVENTION

According to embodiments of the present invention, a method and astructure for forming thin film semiconductor materials for photovoltaicapplications are provided. More particularly, the present inventionprovides a method and structure for forming semiconductor materials usedfor the manufacture of high efficiency photovoltaic cells. Merely by wayof example, the present method and materials include absorber materialsmade of copper indium disulfide species, copper tin sulfide, irondisulfide, or others for single junction cells or multi-junction cells.

In a specific embodiment, a method for forming a thin film photovoltaicdevice is provided. The method includes providing a transparentsubstrate comprising a surface region. A first electrode layer is formedoverlying the surface region. The method includes forming a copper layeroverlying the first electrode layer and forming an indium layeroverlying the copper layer to form a multi-layered structure. In aspecific embodiment, the method includes subjecting at least themulti-layered structure to a thermal treatment process in an environmentcontaining a sulfur bearing species. The method forms a copper indiumdisulfide material from at least the thermal treatment process of themulti-layered structure. In a specific embodiment, the copper indiumdisulfide material comprising a copper-to-indium atomic ratio rangingfrom about 1.2:1 to about 2:1 and a thickness of a substantially coppersulfide material having a copper sulfide surface region. The methodincludes removing the thickness of the copper sulfide material to exposea surface region having a copper poor surface. The copper poor surfacecomprises a copper to indium atomic ratio of less than about 0.95:1. Themethod subjects the copper poor surface to a metal cation species toconvert the copper poor surface from an n-type semiconductorcharacteristic to a p-type semiconductor characteristic. The methodfurther subjects the copper poor surface to a treatment process during atime period associated with the subjecting of the copper poor surfacewith the metal species. A window layer is formed overlying the copperindium disulfide material.

In an alternative embodiment, a method for forming a thin filmphotovoltaic device is provided. The method includes providing atransparent substrate comprising a surface region. A first electrodelayer is formed overlying the surface region. In a specific embodiment,the method forms a copper indium material comprising an atomic ratio ofCu:In ranging from about 1.35:1 to about 1.60:1 by at least sputtering atarget comprising an indium copper material. The method subjects thecopper indium material to a first thermal treatment process in anenvironment containing a sulfur bearing species to form a copper indiumdisulfide material from at least the first thermal treatment process ofthe copper indium material in a specific embodiment. In a specificembodiment, a copper poor copper indium disulfide material is formedwithin a portion of the copper indium disulfide material. The copperpoor copper indium disulfide material has an atomic ration of Cu:In ofabout 0.99 and less. In a specific embodiment, the method includescompensating the copper poor copper indium disulfide material using ametal cation species to change in characteristic from an n-type to ap-type. The method further forms a window layer overlying the copperindium disulfide material.

In yet alternative embodiment, a method for forming a thin filmphotovoltaic device is provided. The method includes providing atransparent substrate comprising a surface region. A first electrodelayer is formed overlying the surface region The method includes forminga chalcopyrite material overlying the electrode layer. In a specificembodiment, the chalcopyrite material comprises at least a copper poorcopper indium disulfide material. The copper poor copper indiumdisulfide material includes a copper poor copper indium disulfidematerial surface. The copper poor copper indium disulfide surface has anatomic ratio of Cu:In of about 0.99 and less in a specific embodiment.The method includes compensating the copper poor copper indium disulfidematerial using a metal cation species to change in the copper poorcopper indium disulfide material from an n-type semiconductorcharacteristic a p-type semiconductor characteristic in a specificembodiment. The method forms a window layer overlying the chalcopyritematerial and forms a second electrode layer overlying the window layer.

In still yet alternative embodiment, a thin film photovoltaic device isprovided. The thin film photovoltaic device includes a substrate. Thesubstrate includes a surface region. A first electrode layer overliesthe surface region. A chalcopyrite material overlies the first electrodelayer. In a specific embodiment, the thin film photovoltaic deviceincludes a copper poor copper indium disulfide surface having an atomicratio of Cu:In of about 0.99 and less. The thin film photovoltaic deviceincludes a compensating metal species provided within one or moreportions of the copper poor copper indium disulfide surface to changethe copper poor copper indium disulfide surface from an n-typesemiconductor characteristic to a p-type semiconductor characteristic ina specific embodiment. The semiconductor includes a window layeroverlying the copper indium disulfide material and a second electrodelayer overlying the window layer.

In a specific embodiment, the present invention provides a method forforming a thin film photovoltaic device. The method includes providing atransparent substrate (e.g., soda lime glass, water white glass)comprising a surface region. The method forms a first electrode layeroverlying the surface region and forms a copper containing layeroverlying the first electrode layer. In a specific embodiment, thecopper containing layer may also contain other metal species, e.g.,gallium, aluminum, zinc-tin, and indium. The method includes forming anindium layer overlying the copper layer to form a multi-layeredstructure. The method subjects at least the multi-layered structure to athermal treatment process in an environment containing a sulfur bearingspecies. Next, the method forms a copper indium disulfide material fromat least the thermal treatment process of the multi-layered structure.The copper indium disulfide material comprises a copper-to-indium atomicratio ranging from about 1.2:1 to about 2:1 and a thickness ofsubstantially copper sulfide material having a copper sulfide surfaceregion. The method removes the thickness of the copper sulfide materialto expose a surface region having a copper poor surface comprising acopper to indium atomic ratio of less than about 0.95:1 or other surfaceimperfection or characteristic or defects, e.g., smaller grains,impurities, surface texture. The method includes subjecting the copperpoor surface (or other surface imperfection, characteristic, or defects)to a metal cation species including at least an indium species and formsa window layer overlying the copper indium disulfide material.

Many benefits are achieved by ways of present invention. For example,the present invention uses starting materials that are commerciallyavailable to form a thin film of semiconductor bearing materialoverlying a suitable substrate member. The thin film of semiconductorbearing material can be further processed to form a semiconductor thinfilm material of desired characteristics, such as atomic stoichiometry,impurity concentration, carrier concentration, doping, and others. In aspecific embodiment, the band gap of the resulting copper indiumdisulfide material is about 1.55 eV. Additionally, the present methoduses environmentally friendly materials that are relatively less toxicthan other thin-film photovoltaic materials. In a preferred embodiment,the present method and resulting structure is substantially free from aparasitic junction on an absorber layer based upon a copper poorchalcopyrite material. Also in a preferred embodiment, the open circuitvoltage of the chalcopyrite material such as copper indium disulfideranges from about 0.8 volts and greater and preferably 0.9 volts andgreater or 1.0 volts and greater up to 1.2 volts. Depending on theembodiment, one or more of the benefits can be achieved. These and otherbenefits will be described in more detailed throughout the presentspecification and particularly below.

Merely by way of example, the present method and materials includeabsorber materials made of copper indium disulfide species, copper tinsulfide, iron disulfide, or others for single junction cells or multijunction cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-8 are schematic diagrams illustrating a method and structure forforming a thin film photovoltaic device according to an embodiment ofthe present invention;

FIGS. 9-11 are simplified diagrams illustrating a method and structurefor forming a thin film photovoltaic device including metal speciestreatment according to an embodiment of the present invention; and

FIGS. 12, 13, and 14 are plots of experimental results (Voc, Jsc,efficiency) according to one or more embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

According to embodiments of the present invention, a method and astructure for forming semiconductor materials for photovoltaicapplications are provided. More particularly, the present inventionprovides a method for manufacturing thin film photovoltaic devices.Merely by way of example, the method has been used to provide a copperindium disulfide thin film material for high efficiency solar cellapplication. But it would be recognized that the present invention has amuch broader range of applicability, for example, embodiments of thepresent invention may be used to form other semiconducting thin films ormultilayers comprising iron sulfide, cadmium sulfide, zinc selenide, andothers, and metal oxides such as zinc oxide, iron oxide, copper oxide,and others.

FIGS. 1-8 are simplified schematic diagrams illustrating a method forforming a thin film photovoltaic device according to an embodiment ofthe present invention. These diagrams are merely examples, which shouldnot unduly limit the claims herein. One skilled in the art wouldrecognize other variations, modifications, and alternatives. As shown inFIG. 1, a substrate 110 is provided. In an embodiment, the substrate 110includes a surface region 112 and is held in a process stage within aprocess chamber (not shown). In another embodiment, the substrate 110 isan optically transparent solid material. For example, substrate 110 canuse material such as glass, quartz, fused silica, or plastic, or metal,or foil, or semiconductor, or composite materials. Depending upon theembodiment, the substrate can be a single material, multiple materials,which are layered, composites, or stacked, including combinations ofthese, and the like. Of course there can be other variations,modifications, and alternatives.

As shown in FIG. 2, the present method forms an electrode layer 120overlying a surface region 112 of substrate 110. The electrode layer canbe a suitable metal material, a semiconductor material or a transparentconducting oxide material, or a combination. Electrode layer 120 can beformed using techniques such as sputtering, evaporation (e.g., usingelectron beam), electro-plating, or a combination of these, and thelike, according to a specific embodiment. Preferably, the electrodelayer is characterized by a resistivity of about 10 Ohm/cm² to 100Ohm/cm² and less according to a specific embodiment. In a specificembodiment, the electrode layer can be made of molybdenum or tungsten.The electrode layer can have a thickness ranging from about 100 nm to 2micron in a specific embodiment, but can also be others depending on theapplication. Other suitable materials such as copper, chromium,aluminum, nickel, or platinum, and the like may also be used. Of course,there can be other variations, modifications, and alternatives.

As shown in FIG. 3, a copper layer 130 is formed overlying the electrodelayer. In particular, copper (Cu) layer 130 is formed overlying theelectrode layer 120. For example, the copper layer can be formed using asputtering process using a suitable copper target. In one example, a DCmagnetron sputtering process can be used to deposit Cu layer 130 ontothe electrode layer 120. The sputtering process is performed under asuitable pressure and temperature. In a specific embodiment, thesputtering process can be performed under a deposition pressure of about6.2 mTorr. In a specific embodiment, the deposition pressure may becontrolled using Ar gas. In a specific embodiment, an Ar gas flow rateof about 32 sccm is used to achieve the desired deposition pressure.Deposition can be provided at room temperature without heating thesubstrate. Of course, minor heating may result due to plasma generatedduring deposition. Additionally, a DC power supply of about 115 W may beused for the sputtering process. Depending on the embodiment, DC powerranging from 100 W to 150 W may be used depending on the specificmaterials used. A deposition time for a Cu layer of 330 nm thickness isabout 6 minutes or more under the described deposition condition. Ofcourse, the deposition condition can be varied and modified according toa specific embodiment. One skilled in the art would recognize othervariations, modifications, and alternatives.

In a preferred embodiment, the method includes forming a barrier layer125 overlying the electrode layer to form an interface region betweenthe electrode layer and the copper layer. In a specific embodiment, theinterface region is maintained substantially free from a metal disulfidelayer having a semiconductor characteristic that is different from acopper indium disulfide material formed during later processing steps.Depending upon the embodiment, the barrier layer has suitable conductivecharacteristics and can be reflective to allow electromagnetic radiationto reflect back into a photovoltaic cell or can also be transparent orthe like. In a specific embodiment, the barrier layer is selected fromplatinum, titanium, chromium, or silver. Of course, there can be othervariations, modifications, and alternatives.

Referring now to FIG. 4. The method forms an indium layer 140 overlyingcopper layer 130. The indium layer is deposited over the copper layerusing a sputtering process in a specific embodiment. In a specificembodiment, the indium layer can be deposited using a DC magnetronsputtering process under a similar condition for depositing the Culayer. The deposition time for the indium layer may be shorter than thatfor Cu layer. As merely an example, 2 minutes and 45 seconds may beenough for depositing an In layer of about 410 nm in thickness accordingto a specific embodiment. In another example, the indium layer can bedeposited overlying the copper layer using an electro-plating process,or others dependent on specific embodiment.

FIGS. 1 through 4 illustrate a method of forming a multilayeredstructure 150 comprising copper and indium on a substrate for a thinfilm photovoltaic device according to an embodiment of the presentinvention. In a specific embodiment, copper layer 130 and indium layer140 are provided in a certain stoichiometry to allow for a Cu-richmaterial with an atomic ratio of Cu:In greater than 1 for themultilayered structure 150. For example, the atomic ratio Cu:In can bein a range from about 1.2:1 to about 2.0:1 or larger depending upon thespecific embodiment. In an implementation, the atomic ratio of Cu:In isbetween 1.35:1 and 1.60:1. In another implementation, the atomic ratioof Cu:In is selected to be about 1.55:1. In a preferred embodiment, theatomic ratio Cu:In is provided such that Cu is limiting, which consumesessentially all of the indium species provided for the resultingstructure. In a specific embodiment, indium layer 140 is provided tocause substantially no change in the copper layer 130 formed untilfurther processing. In another embodiment, indium layer 140 can be firstdeposited overlying the electrode layer followed by deposition of thecopper layer 130 overlying the indium layer. Of course there can beother variations, modifications, and alternatives.

As shown in FIG. 5, multilayered structure 150 is subjected to a thermaltreatment process 200. In a specific embodiment, the thermal treatmentprocess is provided in an environment containing at least a sulfurbearing species 210. The thermal treatment process is performed at anadequate pressure and temperature. In a specific embodiment, the thermaltreatment process is provided at a temperature ranging from about 400Degrees Celsius to about 600 Degrees Celsius. In certain embodiment, thethermal treatment process can be a rapid thermal process provided at thetemperature range for about three to fifteen minutes. In one example,the sulfur bearing species is in a fluid phase. As an example, thesulfur bearing species can be provided in a solution, which hasdissolved Na₂S, CS₂, (NH₄)₂S, thiosulfate, among others. In anotherexample, the sulfur bearing species 210 is gas phase hydrogen sulfide.In other embodiments, the sulfur bearing species can be provided in asolid phase. As merely an example, elemental sulfur can be heated andallowed to vaporize into a gas phase, e.g., as S_(n). In a specificembodiment, the gas phase sulfur is allowed to react to theindium/copper layers. In other embodiments, combinations of sulfurspecies can be used. Of course, the thermal treatment process 200includes certain predetermined ramp-up and ramp down time and ramp-upand ramp-down rate. For example, the thermal treatment process is arapid thermal annealing process. In a specific embodiment, the hydrogensulfide gas is provided through one or more entry valves with flow ratecontrols into the process chamber. The hydrogen sulfide gas pressure inthe chamber may be controlled by one or more pumping systems or others,depending on the embodiment. Of course, there can be other variations,modifications, and alternatives.

In a specific embodiment, the sulfur bearing species can be provided asa layer material overlying the indium and copper layers or copper andindium layers. In a specific embodiment, the sulfur bearing species isprovided as a thin layer or as a patterned layer. Depending upon theembodiment, the sulfur bearing species can be provided as a slurry, apowder, a solid material, a gas, a paste, or other suitable form. Ofcourse, there can be other variations, modifications, and alternatives.

Referring to FIG. 5, the thermal treatment process 200 causes a reactionbetween copper indium material within the multilayered structure 150 andthe sulfur bearing species 210, thereby forming a layer of copper indiumdisulfide material (or a copper indium disulfide thin film) 220. In oneexample, the copper indium disulfide material or copper indium disulfidethin film 220 is formed by incorporating sulfur ions/atoms stripped ordecomposed from the sulfur bearing species into the multilayeredstructure 150 with indium atoms and copper atoms mutually diffusedtherein. In an embodiment, the thermal treatment process 200 results ina formation of a cap layer 221 overlying the transformed copper indiumdisulfide material 220. The cap layer contains a thickness ofsubstantially copper sulfide material but substantially free of indiumatoms. The cap layer includes a surface region 225. In a specificembodiment, the formation of this cap layer is under a Cu-richconditions for the Cu—In bearing multilayered structure 150. Dependingon the embodiment, the thickness of the copper sulfide material 221 ison an order of about five to ten nanometers and greater based onoriginal multilayered structure 150 with indium layer 140 overlyingcopper layer 130. Of course, there can be other variations,modifications, and alternatives.

FIG. 6 is a schematic diagram illustrating a process of the method forforming a thin film photovoltaic device according to an embodiment ofthe present invention. The diagram is merely an example, which shouldnot unduly limit the claims herein. One skilled in the art wouldrecognize other variations, modifications, and alternatives. As shown inFIG. 6, a dip process 300 is performed to the copper sulfide material221 that covers the copper indium disulfide thin film 220. Inparticular, the dip process is performed by exposing the surface region225 to a solution of potassium cyanide 310 in a specific embodiment. Ina specific embodiment, the solution of potassium cyanide has aconcentration of about 1 weight % to about 10 weight % according to aspecific embodiment. The solution of potassium cyanide acts as anetchant that is capable of selectively removing copper sulfide material221 from the surface region of the copper indium disulfide material. Theetching process starts from the exposed surface region 225 and down tothe thickness of the copper sulfide material 221 and substantiallystopped at the interface between the copper sulfide material 221 andcopper indium disulfide material 220. As a result the copper sulfide caplayer 221 is selectively removed by the etching process to exposesurface region 228 of the copper indium disulfide thin film materialaccording to a specific embodiment. In a preferred embodiment, the etchselectivity is about 1:100 or more between copper sulfide and copperindium disulfide material. In other embodiments, other selective etchingspecies can be used. In a specific embodiment, the etching species canbe hydrogen peroxide. In other embodiments, other techniques includingelectro-chemical etching, plasma etching, sputter-etching, or anycombination of these may be used. In a specific embodiment, the coppersulfide material can be mechanically removed, chemically removed,electrically removed, or any combination of these, and others. In aspecific embodiment, an absorber layer made of copper indium disulfidecan have a thickness of about 1 to 10 microns, but can be others. Ofcourse, there can be other variations, modifications, and alternatives.

As shown in FIG. 7, the method further process the copper indiumdisulfide material to form a p-type copper indium disulfide film 320 ina specific embodiment. In certain embodiments, the as-formed copperindium disulfide material may have a desirable p-type semiconductingcharacteristic. In a specific embodiment, copper indium disulfidematerial 220 is subjected to a doping process to adjust p-type impurityconcentration therein for the purpose of optimizing I-V characteristicof the high efficiency thin film photovoltaic devices. In an example,aluminum species are allowed to mix into the copper indium disulfidematerial 220. In another example, the copper indium disulfide material220 is mixed with a copper indium aluminum disulfide material. Ofcourse, there can be other variations, modifications, and alternatives.

Subsequently, a window layer 310 is formed overlying the p-type copperindium disulfide material 320. The window layer can be selected from agroup consisting of a cadmium sulfide (CdS), a zinc sulfide (ZnS), zincselenium (ZnSe), zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), orothers. In certain embodiments, these materials may be doped with one ormore suitable impurities to form an n′ type semiconductor material. Thewindow layer and the absorber layer forms a PN junction associated witha photovoltaic cell. The window layer is heavily doped to form a n⁺-typesemiconductor layer in a preferred embodiment. In one example, indiumspecies are used as the doping material to cause formation of then⁺-type characteristic associated with the window layer 310. In anotherexample, the doping process is performed under suitable conditions. In aspecific embodiment, the window layer can use an aluminum doped ZnOmaterial. The aluminum doped ZnO material can range from about 200 nm toabout 500 nanometers in a specific embodiment. Of course, there can beother variations, modifications, and alternative

Referring to FIG. 8, the method forms a conductive layer 330 overlying aportion of a first surface region of the window layer 310. Theconductive layer forms a top electrode layer for the photovoltaicdevice. In one embodiment, the conductive layer 330 is a transparentconductive oxide (TCO). For example, the TCO can be selected from agroup consisting of In₂O₃:Sn (ITO), ZnO:Al (AZO), SnO₂:F (TFO), and thelike, but can be others. In another embodiment, the TCO layer isprovided in a certain predetermined pattern to maximize the fill factorand conversion efficiency of the photovoltaic device. In a specificembodiment, the TCO can also function as a window layer, whichessentially eliminates a separate window layer. Of course there can beother variations, modifications, and alternatives.

In a preferred embodiment, the present method maintains an interfaceregion between the electrode layer and the copper indium disulfidematerial substantially free from a metal disulfide layer havingdifferent semiconductor characteristics from the copper indium disulfidematerial. Depending upon the type of electrode material, the metaldisulfide layer is selected from molybdenum disulfide layer or the like.In a specific embodiment, the interface region is characterized by asurface morphology substantially capable of preventing any formation ofthe metal disulfide layer, which is characterized by a thickness ofabout 5 nanometers to about 10 nanometers. In a preferred embodiment,the present method includes a thermal process during at least themaintaining process or a portion of the maintaining process of at least300 Degrees Celsius and greater to prevent any formation of the metaldisulfide layer, which can be a molybdenum disulfide or like layer. Ofcourse, there can be other variations, modifications, and alternatives.

In a specific embodiment, the present invention provides a method forforming a thin film photovoltaic device, which is outlined below.

-   -   1. Start;    -   2. Provide a transparent substrate comprising a surface region;    -   3. Form a first electrode layer overlying the surface region;    -   4. Form a copper layer overlying the first electrode layer;    -   5. Form an indium layer overlying the copper layer to form a        multi-layered structure (alternatively indium is formed first or        a multiple layers are sandwiched together);    -   6. Subject at least the multi-layered structure to a thermal        treatment process in an environment containing a sulfur bearing        species;    -   7. Form a copper indium disulfide material from at least the        treatment process of the multi-layered structure, the copper        indium disulfide material comprising a copper-to-indium atomic        ratio ranging from about 1.2:1 to about 2:1 or 1.35:1 to about        1.60:1 and a thickness of substantially copper sulfide material        having a copper sulfide surface region;    -   8. Remove the thickness of the copper sulfide material to expose        a surface region having a copper poor surface comprising a        copper to indium atomic ratio of less than about 0.95:1 or        0.99:1;    -   9. Subject the copper poor surface to a metal species to convert        the copper poor surface from an n-type characteristic to a        p-type characteristic;    -   10. Subject the copper poor surface to a treatment process        during a time period associated with the subjecting of the        copper poor surface with the metal species;    -   11. Form a window layer overlying the copper indium disulfide        material;    -   12. Form a second electrode layer; and    -   13. Perform other steps, as desired.

The above sequence of steps provides a method according to an embodimentof the present invention. In a specific embodiment, the presentinvention provides a method and resulting photovoltaic structure freefrom parasitic junction regions in the absorber layer, which impairperformance of the resulting device. Other alternatives can also beprovided where steps are added, one or more steps are removed, or one ormore steps are provided in a different sequence without departing fromthe scope of the claims herein. Details of the present method andstructure can be found throughout the present specification and moreparticularly below.

FIGS. 9-11 are simplified diagrams illustrating a method and structurefor forming a thin film photovoltaic device including metal speciestreatment according to an embodiment of the present invention. Thesediagrams are merely examples, which should not unduly limit the scope ofthe claims herein. One of ordinary skill in the art would recognizeother variations, modifications, and alternatives. In a specificembodiment, the present method begins with a partially completedphotovoltaic device 900. As shown, the device includes a transparentsubstrate 901 comprising a surface region, although other substrates canbe used. The device also includes a first electrode layer 903 overlyingthe surface region. In a specific embodiment, the first electrode layercan be any conductive material including conductive metals, oxides, andsemiconductor or combinations of these, as well as any materialdescribed herein and outside of the present specification.

In a specific embodiment, the photovoltaic device includes achalcopyrite material, which acts as an absorber for the photovoltaicdevice. As shown, the chalcopyrite material can include, among others,copper indium disulfide material, copper indium aluminum disulfide,copper indium gallium disulfide, combinations of these, and others. in aspecific embodiment, the chalcopyrite has a thin layer of copper sulfide907, which has been previously described, as may remain as a residue orfixed material. Of course, there can be other variations, modifications,and alternatives.

Referring to FIG. 10, the method selectively removes the thin layer ofcopper sulfide. In a specific embodiment, the thin layer is removed 909using a solution of potassium cyanide (KCN) or other suitable technique,e.g., dry etching, plasma etching, sputtering. In a specific embodiment,the method may cause formation of a copper poor surface region 1001. Ina specific embodiment, the copper poor surface is characterized by acopper to indium atomic ratio of less than about 0.95:1 or 0.99:1. In aspecific embodiment, the copper poor surface region is characterized asan n-type material, which forms a parasitic junction with the p-typecopper indium disulfide material, which can be rich in copper. Theparasitic junction leads to poor or inefficient device performance. Ofcourse, there can be other variations, modifications, and alternatives.

In a preferred embodiment, the present method subjects the copper poorsurface to an ionic species such as a metal cation species to convertthe copper poor surface from an n-type characteristic to a p-typecharacteristic 1101, which behaves like a normal copper indium disulfidesurface, as shown in FIG. 11. In a preferred embodiment, the metalspecies is a metal cation ion, which can be derived from transitionmetals such as Zn²⁺, Fe⁺, Fe²⁺, Ni⁺, Mn²⁺, Cr³⁺, Ti⁴⁺, V^(n+) (n=2, 3,4, 5), Sc³⁺, Ag⁺, Pd²⁺, Y³⁺, Zr, Mo²⁺, or other suitable transitionmetal salts and the like. In an alternative embodiment, the metalspecies can be derived from alkaline metal cations such as Li⁺, K⁺, Rb⁺,and the like. In certain embodiments, the metal species can be derivedfrom an alkaline earth metal cations such as Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, andthe like. In a specific embodiment, the subjecting the copper poorsurface includes a thermal treatment process during a time periodassociated with the subjecting of the copper poor surface with the ionicspecies. In a specific embodiment, the thermal treatment process canrange in temperature from about 100 Degrees Celsius to about 500 DegreesCelsius, but can be others. Additionally, the thermal treatment processoccurs for a time period ranging from a few minutes to about ten minutesto an hour or so. Of course, there can be other variations,modifications, and alternatives.

In a specific embodiment, the metal species, can be applied using one ormore techniques. These techniques include deposition, sputtering, spincoating, spraying, spray pyrolysis, dipping, electro deposition,painting, ink jet coating, sprinkling, any combination of these, andothers. In some embodiments, the metal species can be diffused from anoverlying material, which can be an electrode layer or molybdenum orother suitable material. Alternatively, the metal species can bediffused from a piece of metal material or the like via a vapor phase.In a specific embodiment, the ionic species such as the metal ions canbe diffused in vapor phase, but can be others, for short periods oftime. In a specific embodiment, the treatment process passivates thesurface at the heterojunction or the like, which facilitates carrierseparation and transport. Additionally, the present treatment processcan also generate desired conduction band offset, commonly called CBO.Of course, there can be other variations, modifications, andalternatives.

In a specific embodiment, the method includes forming a window layeroverlying the copper indium disulfide material. The method also forms anelectrode layer overlying the window layer. Depending upon theembodiment, the photovoltaic cell can be coupled to a glass ortransparent plate or other suitable member. Alternatively, thephotovoltaic cell can be coupled to another cell, e.g., a bottom cell,to form a tandem or multi junction cell. Again, there can be othervariations, modifications, and alternatives.

FIGS. 12, 13, and 14 are plots of experimental results (Voc, Jsc, andefficiency) according to one or more embodiments of the presentinvention. These diagrams are merely examples, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize other variations, modifications, and alternatives. Also,these are experimental results and should not unduly limit the scope ofthe claims herein. The experimental results demonstrate the operation ofthe present method and resulting devices, which achieved improvedresults.

According to the present experiments, a transparent substrate comprisinga surface region was used. That is, the transparent substrate was waterwhite or soda lime glass or can be others. A first electrode layer madeof aluminum doped zinc oxide, commonly called AZO, was formed usingsputter deposition overlying the surface region. The experiment alsoused a copper and gallium containing layer overlying the first electrodelayer and an indium layer overlying the copper and gallium containinglayer to form a multi-layered structure. The copper/gallium layer andthe indium layer were sputter deposited under standard conditions usingat least an argon species plasma. Next, the method subjects at least themulti-layered structure to a thermal treatment process at an elevatedtemperature ranging from about 250 to about 350 Degrees Celsius andhigher in an environment containing a sulfur bearing species to form acopper indium gallium disulfide material from at least the thermaltreatment process of the multi-layered structure.

I believe the copper indium gallium disulfide material comprising acopper-to-indium and gallium (Cu/In+Ga) atomic ratio ranging from about1.2:1 to about 2:1 and a thickness of a substantially copper sulfidematerial having a copper sulfide (Cu_(x)S, where x=1 to 2, for example)surface region. Next, I removed the thickness of the copper sulfidematerial using KCN aqueous solution to expose a surface region having acopper poor surface. The copper poor surface comprises a copper toindium atomic ratio of less than about 0.95:1, which often leads to poordevice performance and may be an n-type material, which also leads topoor device performance.

In this experiment, the copper poor surface was subjected to a metalcation species to possibly convert the copper poor surface from ann-type semiconductor characteristic to a p-type semiconductorcharacteristic. As an example, indium trichloride (InCl₃) was used asthe source of the metal cation species. As an example, the indiumtrichloride was dissolved in water at a concentration ranging from about0.05 molar to about 0.1 molar, but can be others. The copper poorsurface was subjected to the aqueous solution including the indiumspecies for a suitable amount of time. Optionally, the copper poorsurface may be subjected to a treatment process at a temperatureassociated with the subjecting of the copper poor surface with the metalspecies. I believe that the indium species replaced missing copper fromthe upper surface of the copper poor surface. A window layer made ofcadmium sulfide is formed overlying the copper indium disulfidematerial. Details of the experimental results are provided below.

As shown, FIG. 12 illustrates open circuit voltage (Voc) plotted againstruns (1) and (2). Each of the runs includes a batch with InCl₃ andwithout InCl₃ according to one or more embodiments. As can be clearlyseen, the batch using the InCl₃ has a Voc higher by about 0.3 volts,which is significant. Similarly, the short circuit junction current Jscis also higher in both batches treated with InCl₃. See FIG. 13, whichplots short circuit current density in (mA/cm²) plotted against runs (1)and (2). More significantly, FIG. 14 illustrates light scan efficiencyagainst runs (1) and (2). As shown, average efficiencies of the InCl₃treated batches were respectively 10.25% and 9.75% for batches 1 and 2,while the respective non treated batches were 8.75% and 8.50% onaverage. As shown, treatment using a metal cation species improvedphotovoltaic device performances. Of course, there can be othervariations, modifications, and alternatives.

Although the above has been illustrated according to specificembodiments, there can be other modifications, alternatives, andvariations. Additionally, although the above has been described in termsof copper indium disulfide, other like materials such as copper indiumgallium disulfide, copper indium aluminum disulfide, combinationsthereof, and others can be used. Other materials may include CuGaS₂,CuInSe₂, Cu(InGa)Se₂, Cu(InAl)Se₂, Cu(In,Ga)SSe, combinations of these,and the like. In a specific embodiment, the metal cation compensates forand/or passivates the Cu-poor condition. This can be provided, in thebroadest terms, by using metal salts or cation-anion compounds whosecation is based on alkali metals (e.g., Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺),alkaline earth metals (e.g., Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺), transition metals(e.g., cations of various valence states of Cu, Cd, Zn, Ni, Mn, Fe, Co,Cr, V, Ti, Sc, Ag, Mo, W, Pd, Hg, Ta, Pt, Au, Y, Zr, Ru, Rh, Ir, Os,etc.), and possibly even Group III metals (e.g., cations of variousvalence states of Al, Ga, or In), combinations of these, and others. Ina specific embodiment, the indium cation can be derived from a suitablecompound such as, for example, InCl₃, among others. Additionally, asused herein, the term copper indium disulfide is to be interpretedbroadly and may include other elements and is not specifically limitedto the recited species according to one or more embodiments. Likewise,the other materials and/or compounds are also not limited, but should beinterpreted by ordinary meaning according to one or more embodiments. Ina specific embodiment, Na⁺ cation may be particularly good due to it'srelative size, e.g., K⁺ ion may be effective, but due to its largersize, may diffuse slower than Na⁺ under the same processing conditions.In a specific embodiment, the counterpart anion in the salt, in thebroadest terms, are chalcogens (e.g., oxides, sulfides, selenides,tellurides), halogens (e.g., fluorides, chlorides, bromides, iodides),organic and inorganic molecular anions (e.g., acetates, carboxylates,cyanides, oxalates, benzoates, azides, anions derived from amides,organic chelates (e.g., EDTA), inorganic chelates, phosphates, sulfates,arsenates, etc.), and possibly Group V anions (e.g., nitrides,phosphides, arsenides, antimonides), combinations of these, and others.It is understood that the examples and embodiments described herein arefor illustrative purposes only and that various modifications or changesin light thereof will be suggested to persons skilled in the art and areto be included within the spirit and purview of this application andscope of the appended claims.

1. A method for forming a thin film photovoltaic device, the methodcomprising: providing a transparent substrate comprising a surfaceregion; forming a first electrode layer overlying the surface region;forming a copper layer overlying the first electrode layer; forming anindium layer overlying the copper layer to form a multi-layeredstructure; subjecting at least the multi-layered structure to a thermaltreatment process in an environment containing a sulfur bearing species;forming a copper indium disulfide material from at least the thermaltreatment process of the multi-layered structure, the copper indiumdisulfide material comprising a copper-to-indium atomic ratio rangingfrom about 1.2:1 to about 2:1 and a thickness of substantially coppersulfide material having a copper sulfide surface region; removing thethickness of the copper sulfide material to expose a surface regionhaving a copper poor surface comprising a copper to indium atomic ratioof less than about 0.95:1; subjecting the copper poor surface to a metalcation species to convert the copper poor surface from an n-typesemiconductor characteristic to a p-type semiconductor characteristic;subjecting the copper poor surface to a treatment process during a timeperiod associated with the subjecting of the copper poor surface withthe metal cation species; and forming a window layer overlying thecopper indium disulfide material.
 2. The method of claim 1 wherein thesubjecting of the metal cation species is provided by at least oneprocess selected from spin coating, spraying, spray pyrolysis,pyrolysis, dipping, deposition, sputtering, or electrolysis.
 3. Themethod of claim 1 wherein the metal cation species comprises atransition metal cation, an alkaline metal cation or an alkaline earthmetal cation.
 4. The method of claim 1 wherein the removing comprisesusing a solution of potassium cyanide to selectively remove thethickness of copper sulfide material.
 5. The method of claim 1 whereinthe window layer is selected from a group consisting of a cadmiumsulfide, a zinc sulfide, zinc selenide, zinc oxide, or zinc magnesiumoxide.
 6. The method of claim 1 wherein the treatment process of thecopper poor surface comprises a thermal process ranging from about 100Degrees Celsius to about 500 Degrees Celsius.
 7. The method of claim 1wherein the forming of the copper layer is provided by a sputteringprocess or plating process.
 8. The method of claim 1 wherein the metalcation species compensates for any missing copper in the copper poorsurface.
 9. The method of claim 1 wherein the forming of the indiumlayer is provided by a sputtering process.
 10. The method of claim 1wherein the forming of the indium layer is provided by a platingprocess.
 11. The method of claim 1 wherein the copper indium disulfidehas a p-type semiconductor characteristic.
 12. The method of claim 1wherein the window layer comprises an n⁺-type semiconductorcharacteristic.
 13. The method of claim 1 further comprising introducingan indium species in the window layer to cause formation of an n⁺-typesemiconductor characteristic.
 14. The method of claim 1 wherein thecopper indium disulfide is mixed with a copper indium aluminum disulfideor copper indium gallium disulfide.
 15. The method of claim 1 whereinthe sulfur bearing species comprise hydrogen sulfide in fluid phase. 16.A method for forming a thin film photovoltaic device, the methodcomprising: providing a transparent substrate comprising a surfaceregion; forming a first electrode layer overlying the surface region;forming a copper indium material comprising an atomic ratio of Cu:Inranging from about 1.35:1 to about 1.60:1 by at least sputtering atarget comprising an indium copper material; subjecting the copperindium material to a first thermal treatment process in an environmentcontaining a sulfur bearing species; forming a copper indium disulfidematerial from at least the first thermal treatment process of the copperindium material; forming a copper poor copper indium disulfide materialin a surface region of the copper indium disulfide material, the copperpoor copper indium disulfide material having an atomic ration of Cu:Inof about 0.99 and less; compensating the copper poor copper indiumdisulfide material using a metal cation species to change incharacteristic from an n-type to a p-type; and forming a window layeroverlying the copper indium disulfide material.
 17. The method of claim16 wherein the compensating is provided by at least one process selectedfrom spin coating, spraying, spray pyrolysis, pyrolysis, dipping,deposition, sputtering, or electrolysis.
 18. The method of claim 16wherein the metal cation species comprises a transition metal cation, analkaline metal cation or an alkaline earth metal cation.
 19. The methodof claim 16 further comprising subjecting at least the copper poorcopper indium disulfide material to a second thermal treatment processranging in temperature from about 100 Degrees Celsius to about 500Degrees Celsius.
 20. The method of claim 16 wherein the window layer isselected from a group consisting of a cadmium sulfide, a zinc sulfide,zinc selenide, zinc oxide, or zinc magnesium oxide.
 21. The method ofclaim 16 further comprising forming a transparent conductive oxideoverlying a portion of the window layer.
 22. The method of claim 16wherein the copper indium disulfide material has a p-type semiconductorcharacteristic.
 23. The method of claim 16 wherein the window layercomprises n+-type semiconductor characteristic.
 24. The method of claim16 further comprising introducing an indium species in the window layerto cause formation of an n+-type semiconductor characteristic.
 25. Themethod of claim 16 wherein the sulfur bearing species comprise hydrogensulfide.
 26. A method for forming a thin film photovoltaic device, themethod comprising: providing a transparent substrate comprising asurface region; forming a first electrode layer overlying the surfaceregion; forming a chalcopyrite material overlying the electrode layer,the chalcopyrite material comprising at least a copper poor copperindium disulfide material including a copper poor copper indiumdisulfide material surface, the copper poor copper indium disulfidesurface having an atomic ratio of Cu:In of about 0.99 and less; andcompensating the copper poor copper indium disulfide material using ametal cation species to change in characteristic from an n-type to ap-type; forming a window layer overlying the chalcopyrite material; andforming a second electrode layer overlying the window layer.
 27. A thinfilm photovoltaic device comprising: a substrate comprising a surfaceregion; a first electrode layer overlying the surface region; achalcopyrite material overlying the first electrode layer; a copper poorcopper indium disulfide surface, the copper poor copper indium disulfidesurface having an atomic ratio of Cu:In of about 0.99 and less; and acompensating metal cation species provided within one or more portionsof the copper poor copper indium disulfide surface to change the copperpoor copper indium disulfide surface from an n-type semiconductorcharacteristic to a p-type semiconductor characteristic; a window layeroverlying the copper indium disulfide material; and a second electrodelayer overlying the window layer.
 28. A method for forming a thin filmphotovoltaic device, the method comprising: providing a transparentsubstrate comprising a surface region; forming a first electrode layeroverlying the surface region; forming a copper containing layeroverlying the first electrode layer; forming an indium layer overlyingthe copper layer to form a multi-layered structure; subjecting at leastthe multi-layered structure to a thermal treatment process in anenvironment containing a sulfur bearing species; forming a copper indiumdisulfide material from at least the thermal treatment process of themulti-layered structure, the copper indium disulfide material comprisinga copper-to-indium atomic ratio ranging from about 1.2:1 to about 2:1and a thickness of substantially copper sulfide material having a coppersulfide surface region; removing the thickness of the copper sulfidematerial to expose a surface region having a copper poor surfacecomprising a copper to indium atomic ratio of less than about 0.95:1;subjecting the copper poor surface to a metal cation species includingat least an indium species; and forming a window layer overlying thecopper indium disulfide material.
 29. The method of claim 28 wherein thecopper containing layer further comprises at least an element selectedfrom at least gallium, aluminum, indium, zinc-tin, and othercombinations of them.